Apparatus for measuring, recording, and controlling dilute dust concentrations



l 5 t 5, w m 0, w 2 w h S 2 L w A 9 T l E R m m n m h R d D m 1 P FApril 13, 1937.

APPARATUS FOR MEASURING, RECORDING, AND CONTROLLING DILUTE DUSTCONCENTRATIONS INVENTOR PH\LIP DR\NKER. W\LL\5 G. HAZARD.

MW 4% I ATTORN EY Aprll 1937- P. DRINKER ET AL 2,076,554

APPARATUS FOR MEASURING, RECORDING. AND CONTROLLING DILUTE DUSTCONCENTRATIONS Filed Jan. 21, 1932'" 2 Sheets-Sheet 2 [104 [106 1 1 5 I59 J T I J T 1 c I 60 g T i NE INVENTOR PHiLlP DRINKER. wmus G. HA'LARD.

ATTORNEY Patented A t. 13, 1937 UNITED, STATES PATENT OFFICE Arrsaa'rcsr01: zzz s uamo, nacoan- IN G, AND CONTROLLING DILUTE CONCENTRATIONSDUST 3 Philip Drinker, Brookline, and Willis Gllpin Hazard, JamaicaPlain, Mass.

Application January 21', 1932, Serial No. 587,854

The present invention relates to apparatus for determining, measuring,recording, controlling and the like, the concentrations! dilute dustsuspended in air and other gases.

5 It is desirable in'many cases to determine the dust content of the airof a room, particularly where the dust concentration may furnish arecognized or suspected dust hazard. If the atmosphere of a factory orother industrial establishment, such as a mine, carries more than acertain, safe proportion of silica dust, for example, the workmenexposed to and breathing the air therein may contract silicosis. ,Suchsilica dust particles, which may be no more than one twenty-five-thousandth of an inch in diameter, are very widely distributed inquarries, subways, foundries, and cutlery establishments, and whereverelse pulverized quartz or sand is abundan't. It is important for thehygienist in- :0 vestigating dust and dust-like, impurities as a menaceto health, in controlling industrial diseases, to be able to determineand record the dust concentration of the atmosphere.

, It is furtherdesirable, in other cases, town- :5 trol industrialprocesses where mixtures of dust and gases are fundamental to thecarrying out of the process; as, for example, in the manufacture of zincoxide and other pigments.

. An object of the invention is to provide novel 30 apparatus forcontinuously measuring, recording or controlling dilute dustconcentrations suspended in air or other gases.

Other and further objects will be explained hereinafter and will beparticularly. pointed out in the appended claim.

The invention will now be explained in connection with the accompanyingdrawings, in which Fig; 1 is a diagrammatic, perspective view ofapparatus and circuits constructed and ar- 40 the present invention;Figs. 2 and 3 are perspec tives of portions of the apparatus shown inFig.

1, parts of the apparatus illustrated in Fig. 3

being shown detached; Fig. 4 is a diagrammatic matic view of calibratingapparatus.

Referring, first, to Fig; 1, the gasto be tested. containing the dilutedust concentration, such as dusty air, is assumed to' be contained in a'mom or other space (not shown). A stream of the dust-laden air or othergasis drawn by a suction pump 26 at' a predetermined station, through apredetermined region or area, shown as a slitvshaped orifice --or jet 2,into an ranged according to a preferred embodiment of;

view of a modification; and Fig. 5 is a diagramair-tight, preferablymetal, casing J, towards (or. 88-14) r Y continuously directed towardthat portion of the film 6 that is disposed over an idler roll i2, whichis disposed at a fixed distance from, and opposite to, the jet 2; andbecause the casing I is air-tight, dust-is prevented from becomingdeposited on the film except at the predetermined station. The slit orjet 2 is very narmw and its area is quite restricted. Its width may, forexample, be of the order of one-tenth of a millimeter. The dust-ladenair enters the casing, therefore, at high velocity.

The chamber may be a humidifying chamber, shown as a tube the walls ofwhich are lined with wet blotting paper to moisten the gas.-

The suction pump 26 is connected by a pipe 28 with an opening of thecasing 4 through an automatic flow-regulator. The automaticflowregulator is designed to maintain a preferably constant air flowthrough'the'jet 2 and may assume many forms. As illustrated in Fig. 1,it comprises a flow meter or mercury manometer 91 and an automatic,constant-flow regulator 99. The manometer 91 measures the negativepressure in the casing 4, and will indicate whether the jet 2 becomesplugged. A mercury manometer 20 may be connected with the casing at I32to aidin controlling the velocity through the jet. A rubber or othergasket I08 between the body of the casing] and its cover iiii maintainsthe casing air tight. Because of the high velocity at which the gasenters the casing 4, the pressure of the gas traveling through the jet 2as the theory is understood, becomes greatly reduced, with a resultingfall in temperature and a consequent condensation of the moisture of thegas upon the dust particles. The thus-wet dust particles impinge uponthe fllm B and, if small enough, become deposited thereon. The moistureevaporates, leaving the now-dried dust particles adhering to the film.This theory may not, however, be correct.

Further totheorize, if the particular dust at hand is soluble in water,passage through the humidifying chamber 8 causes saturation of the air,and'the dust deposited on the film 6, further wet by condensation onpassing through the jet in the manner just described, takes the form ofcrystals rather than of the original unchanged particles. To reduce thelikelihood of such a saturated solution, when dealing with a dustsoluble in water, the humidifying chamber is removed. v

- The film 6 may be continuously unwound from a reverse spool i0, andover the roll l2 and guide rolls 3 and I5, by a motor I, acting upon adriving sprocket it through suitable reduction gearing 9. It is thuscaused to travel continuously past the said station over its supportingrolls. The film 8 may be provided with the usual perforations 5 fittingover the teeth of the sprocket wheel i3. The speed 0! travel of the filmmay be, say, twenty centimeters per hour. Alter passing over thesprocket Wheel, the film is wound on a spool H. A spacer film 79 may beunwound from a spool 2i, and wound on the spool ii along with the film5, to space the successive coils of the film 8 and prevent scratchingofi or dislodging the dust therefrom. If it is desired to recorddustiness, or run alarm systems, special lights, motors or the like,without preserving the record, the spacer iilm is may be omitted.

Zine time corresponding to the record may be indicated on the film inany desired manner. It

' is preferred to employ the following expedient.

Periodically the electric suction pump 26 is stopped for a briefinterval, thus permitting a strip of dustless film to pass before awindow id. The light it then shines with its initial undiminishedintensity on the light-sensitive device and the recorder returns tozero. One advantage of this procedure is to check frequently theamplifier and light source for a shift of zero, which may easily occurduring a days run. The pump may be stopped and started in any'desiredmanner, as by a commutator (not shown) mounted on the outside end of theshaft carrying the sprocket i3. As this is driven by the constant speedmotor l, the blank dustless strips on the consequently act as a timerecord.

After traveling past the jet 2, the dust-carrying film it travels in thecasing 4 to the window A beam of light from a lamp it, the intensity ofwhich is maintained constant by adjustment of a rheostat ill, in serieswith a bat- 93 and an ammeter 95, and the rays of which are renderedparallel-rayed by a lens ll, travels through the window it and through asecond window if) to a light-sensitive means, such as a photo-electriccell 25. The beam of light rays may be made rectangular by a diaphragm22, the width of the rectangular beam being the same as that or the dustdeposited on the film 6. Variaticns of the dust concentration depositedon the him 5 are measured by the fluctuations in the intensity of thebeam of light thus transmitted to the cell 25 from the lamp 516 andthrough the windows i i and i8. 4

It is not essential, of course, that all the dust be deposited on themm, but merely that the proportion of the dust so deposited be constantand known.

The output from the light-sensitive cell may be amplified in any desiredmanner. If the beam is uninterrupted, a direct-current amplifier isappropriate. Such a circuit, designed to compensate for changes of theplate battery voltage will now be described.

The light-sensitive cell 24 is connected in the input circuit of asuitable amplifier, which may preferably be constituted of two vacuumtubes 3%, 36 connected in two adjacent arms of a Wheatstone bridge, forreasons hereinafter explained. The other two arms of the bridge areprovided with impedances and 42. Across the output circuits of theamplifier tubes 34, 36, which are energized by a common B battery 33,there may be connected a suitable recorder or recording meter, such, forexample, as the recording potentiometer disclosed in Letters Patent ofthe United States No. 1,356,804, granted October 26, 1930. The recordermay comprise a chart on which a written record is continuously made by amarker or stylus 49 simultaneously with the deposit of dust upon thefilm. In orde to smi ur specimen passes the window It.

the description, the reference numerals is, 20, 3|, 32, 49, 59, 60, 53,St, 65, 66 and 61 are used herein to designate the same or similar partsas are indicated by the said reference numerals in the said LettersPatent. The tubes 34 and 36 have a common filament battery, shown at 25.Grid bias potentials for the two tubes are derived from separate gridbatteries, 43 and 29, respectively. A high grid resistor 8|, and thegrid battery 63, whose potential may be adjusted by the potentiometerG5, are placed in series between the grid and filamentoi tube 34.Current from the light-sensitive cell 23 applied across the resistor 8iproduces a voltage drop and a change of bias on the grid which, in turn,result in a modification of the plate current of the tube 34. Shuntedacross the plates or the two vacuum tubes is a resistor d4 of a fewhundred ohms.

The adjustment and operation of the amplifier is as follows. Initially,when the film 6 interposed between the light source l6 and thelightsensitive device 24 the manner already described, is uncoated withdeposited dust, the movable element ll or the potentiometer is ad justeduntil no current flows through the resistor as registered on therecording meter by the marker or stylus ill. l fhen a dust deposit onthe film 6 decreases the intensity of light transmitted from the lampit, a change in plate current of the tube 3% is effected. Consequently,a current now flows through the resistor 44, causing a voltage drop init, which actuates the marker or stylus W. The magnitude of the voltagedrop in the resistor 64 is thus dependent on the quantity of dustdeposited on the film 6 by the jet 2.

The zero point,-or, the point to which the recorder stylus d9 returnswhen dust-free film passes through the beam or light rays,must remainconstant for several hours, during which measurements are made orcontrol is eflected. To bring this about, the slow running down of theA, B and 0 batteries 25, 38, 29 and 43, and the effects produced byunsteadiness of the amplifier 34, 36 from other sources, must beminimized or compensated for. A chief purpose of the Wheatstone-bridgearrangement is to compensate for the changes in the 3 battery 38. Thedrain on the C batteries 25 and 43 is so slight that the effect producedby their deterioration is negligible. The decline of the A battery 25and the lightsource battery 93 may be minimized by usinglowfilament-current vacuum tubes 34, 36, a low-current lamp l8, say 3cp., and an over-size battery.

Certain other circuit values, such as the highgrid resistor of severalmegohms, are also required to be maintained constant. Difficultiesarising from leakage and extraneous electric fields are met by shieldingand insulating both the light-sensitive cell 24 and the amplifier tubes34, 36, and avoiding the use of long lead wires. With properprecautions, random fluctuations will be minimized from the output, andthe circuits will be sufficiently stable and sensitive.

The apparatus can be so designed that the light-sensitive cell 24 shallcause the recording of the dust concentration simultaneously with thedeposit of the dust, thus to avoid the time lag between the moment ofdepositing a particular specimen of dust passing through the jet 2 andthe record made at the moment when the In practice, however, no serioussources of error are introduced by this time lag.

The marker or stylus 49 and the record controlled by the actuatingdevice 20 may be re-- aovasu placed by any other desired or selectedinstrument, such as signal apparatus for indicating when the dustconcentration exceeds a predetermined value, or any suitable mechanismfor 5 controlling the amount of dust in the air or other gas towhichthejet 2 is exposed. This last may be eilected, for example, by controllingthe degree of ventilation, as by starting or stopping a ventilating fanI90, operated by a motor .0 I02 from relays IM and I06 (Fig. 4), or byopening or closing dampers and the like (not 'shown); or auxiliarydust-removal equipment (not shown) might be operated to reduce the dustconcentration in the vicinity.- The fan I90 i5 may be'eonnected with aventilating duct (not shown). ployed to control automatically anauxiliary ventilating system supplementary to the main exhaust equipmentwhen the dust concentra- 30 tion exceeds a predetermined value.

' The process is without interruption, there being a continuous stream,through the jet 2, of

dust-laden gas, concentrated into measurablequantities, and new dustfrom the gas being 25 continuously deposited on that portion of thecontinuously traveling film which happens to be disposed opposite to thejet 2. Since the area of the jet 2 and the width of the beam of lightrays from the lamp i6 are constant, since the 30 intensity of the saidbeam of light rays is also constant, and assuming that the air flow islikewise constant or its variability is known, the dust content of themedium is directly and continuously determined automatically andrecord'- 35 ed by the marker or stylus l9, assuming that the speed oftravel of the film past the jet 2 and the window I is likewise constant.A definite, continuous record of dustiness in factories, for example, isthus obtainable. The control of the 40 dust content or the gas will alsodepend upon the above factors. By using the direct-reading record,furthermore, the engineer is enabled to determine the degree of successof the ventilating system, whether or not controlled by the appa- 45ratus of the present invention.

The said areas of the jet 2 and the width of the beam of light rays, aswell as the distance of the film-carrying roll I! from the jet 2, may bemade adjustable in any desired way. The

50 width of 'the jet 2 may be adjusted by moving one of the walls orjaws 33 (Fig. 3) thereof to and from the other jaw 35, and securing theadjustable jaw by means screws 31 in slots 39. A spacer it may then becemented or otherwise 5 secured against the jaws 33, 35. The film 6moves along this spacer and is thus located at a predetermined, constantseparation from the jaws 33 and 35 of the jet. The roll I! may beadjusted by mounting it on a slidably adjust- 60 able plate 53. Themovements of the recorder stylus 49 may be calibrated from time to timeby comparison with actual dust concentrations determined by standardmethods oi sanitary air analysis, as described hereinafter, or 'in other65 Ways- In the use or v taken that the type of dust being deposited remains the same. silica dust, for example, obviously do not apply 70 to adust of different color and different particle size, such as lamp black.calibrations are made by comparing the record obtained'against ac- Ifdesired, the invention may be emthis instrument, care must beCalibrations made against I tual dust concentrations determined by anyof the usual dust determining instruments. Different calibration dataare necessary for each type of dust. Whether or not a calibration forone dust can be used on another is best determined by trial. 0

In order to calibrate the record obtained on the film against actualdust concentrations, the most convenient procedures we have found arethe following. A cloud of the dust to be recorded is blown up orgenerated, preferably in a room, cabinet or space 10, Fig. 5, of about1,000 to 3,000 cubic feet in capacity. Although this room need not begas tight, the less it leaks the easier is the calibration. The dustrecorder is connected to this room at 90, Fig. 5, and run in the mannerdescribed. At known times, and at known rates of air fiow, samples ofthe cabinet air are taken at a point 80, Fig. 5, by means of anintermittent dust sampler 82, and the degree of dustiness or dustconcentrations is determined in 'any of the severally known and approvedmethods, such as are described in U. S. Public Health Service BulletinNo. 144, 1925, entitled Comparative Tests of Instruments for DeterminingAtmospheric Dusts. Other methods, such as the dust determination methodof Drinker and Thomson Journal of Industrial Hygiene, 1925, vol. 7, page261, entitled Determination of suspensoids by alternating currentprecipitators, or that of J. S. Owens, entitled "Jet dust countingapparatus, Journal of Industrial Hygiene, 1922-23, vol. 4, page 522,mayalso be used. The results in any case are expressed as either numbersor weights of particles per unit volume of dusty air. As the time atwhich the sample is taken is known, the concentration or degree ofdustiness by one of these methods is compared against dustiness asindicated by the recorder. By comparing the record of the recorder filmwith that of actual determinations by one of the methods described, andmaking these determinations over the range of concentrations desired, anaccurate calibration curve is obtained. From this record, dustconcentrations can be read or recorded continuously.

Other modifications will obviously occur to persons skilled in the art,and all such are considered to'fali within the spirit and scope of theinvention as defined in the appended claim. What is claimed is:

Apparatus of the character described comprising a support, a member uponwhich dust may be deposited movably mounted upon the support, means forcontinuously directing upon the member a stream of air carrying a dilutedust concentration' of predetermined area in cross section at apredetermined station to cause dust from the stream of air to becomedeposited continuously upon the member, means for preventing dust frombecoming deposited upon the member except at the station, means forcontinuously moving the member upon the support past the station, anactuable device for actuating selected instruments, means controlled inaccordance with the amount of dust deposited upon the member from thestream of air for actuating the actuable device, and means forperiodically interrupting the depositing of the dust on the member toindicate time intervals on the member.

PHILIP DRINKER. WILLIS G. HAZARD.

